Module 3- Carbohydrate metabolism Flashcards
major source of energy in the diet
carbs
carbs make up (%) of caloric intake in monogastrics & ruminants
50
what is the most important carb in plants
starch
T or F: lignin is a carb
F
3 roles of carbs in plants
1) tissue synthesis
2) energy reserve
3) structural support
T or F: very little storage of carbs in animals
T
what 3 body compartments hold the little bit of stored carbs
bloodstream, liver & muscle
carbs can make up to what % in animals diets
70%
T or F: less than 1% of carbs are stored in the body
T
how are carbs classified
based on number of sugar units
lactose
glucose + galactose
sucrose
glucose + fructose
maltose
glucose + glucose
what are the 2 most important carb groups from a nutritional & functional standpoint
1) pentose
2) hexoses -> glucose
what configuration of glucose is recognized by the digestive enzymes in the GI tract
D
T or F: animals cannot utilize L forms of glucose
T
3 most important hexoses
1) glucose
2) galactose
3) fructose
2 major end products of fermentative digestion
1) VFA in rumen
2) glucose in small intestine
2 most important pentose sugars. why?
ribose + deoxyribose
- need for DNA/RNA synthesis
adenosine =
ribose & adenine
major function of ribose
structural component of NAD & NADH
NADH is the ( ) form
reduced
riboflavin is a component of ( ) and ( )
FAD & FMN -> co factors in electron transfer REDOX reactions
T or F: ribose can covert tryptophan into niacin
T
glycosidic linkage
OH group on anomeric C
anomeric carbon
carbon double bonded with O2
alpha vs beta glucose
alpha: OH group is on amomeric carbon OPPOSITE side of ring structure
beta: OH group on anomeric carbon is on SAME side of ring structure
what dictates if glycosidic linkage is alpha or beta
orientation of OH group on carbon #1
monogastrics can only digest ( ) linkages
alpha
lactose has ( ) linkage
beta
maltose has ( ) linkage
alpha
partial digestion yields ( ) in small intestine
maltose
( ) is an intermediate in digestion
maltose
3 examples of polysacharides
starch, cellulose & glycogen
2 classes of polysaccharides + examples
1) homo: made of same monosaccharide units (cellulose)
2) hetero: made of diff monosaccharide units (hemicellulose)
2 types of starch granules
1) amylose
2) amylopectin
how do amylose & amylopectin differ?
structure
high amylose = ( ) amylopectin
low
amylose is ( ) digested
slowly
- pulses: peas & lentils
amylopectin is ( ) digested
rapidly, cereal crops
what happens to amylose structure as it is dissolved in water?
the straight unbranched chain turns into a helical structure to reduce surface area for digestive enzymes to digest polysaccharide chains
resistant starch is ( ) in amylose content
higher
amylose structure
long unbranched chains of glucose
- a (1,4) linkage
amylopectin structure
branched chain polymer with a (1,4) and a (1,6) linkages
why is amylopectin digested at a faster rate?
branches = more surface area for enzymes
what is the storage form of glucose in animals
glycogen
T or F: plants have glycogen
F
difference between glycogen storage in liver vs skeletal muscle
liver: glycogen is not used locally
skeletal muscle: glucose is used locally (does not go to other tissues)
cellulose
long linear polymer of repeating glucose
- b (1,4) linkage
difference between cellulose & starch
cellulose: b (1,4) linkage
starch: a (1,4) linkage
hemicellulose
heterogenous group of polysaccharide substances
- b (1,4) linkages
poly-phenolic compound example
lignin
lignin content ( ) as plant matures
increases
hemicellulose has ( ) backbones & side chains
sugar
pectin is not digestible by mammalian enzymes but it is susceptible to
microbial fermentation
b-glucans linkages
b (1,3) + b (1,4)
T or F: cellulose is insoluble in water
T
T or F: b-glucans are water soluble
T
example of soluble fiber
b-glucans
soluble fiber
forms a viscous material in GI tract which reduces penetration of digestive enzymes and reduces digestion
what 2 feeds are high in b-glucans
barley & oats
- must add beta-glucanase to reduce visocity
- only done in monogastric & poultry diets
soluble xylans
form viscous environment that reduces nutrient digestibility
xylanase
breaks down xylans
2 major sources of xylans
barley & wheat
dietary fiber
component of xylan foods that you are eating
-intrinisic component
functional fiber
supplement added into diet
- components: pectins & xylans
2 components of functional fiber
pectins & xylans
why is high viscosity of fibre beneficial in human diets?
1) slows gastric emptying = feel full faster
2) reduces absorption of fat
2 properties of soluble fiber
1) solubility
2) water holding capacity
2 properties of insoluble fiber
1) absorption & binding ability
2) degradability/fermentability
T or F: insoluble fibers act as pre-biotics
T
what type of carbs are the only ones that can be absorbed in monogastric GI tract
monosaccharides
mammalian enzymes can only breakdown what linkages
a (1,4) or a (1,6)
why doesn’t any carb digestion happen in the stomach of monogastrics?
too acidic for salivary amylose to be active
T or F: a (1,6) linkage is not susceptible to salivary amylase but a (1,4) is
T
major enzyme that initiates carb digestion in the mouth in monogastrics
salivary amylase
where can a (1,6) linkages be broken down in monogastrics
small intestine
how are dextrins formed
formed from initial digestion of starch in the mouth
limitation to carb digestion in mouths of monogastrics
short amount of time food stays in the mouth
what is flowing out of the mouth -> stomach during monogastric carb digestion
dextrins & starch (amylose & amylopectin)
stomach pH of monogastrics
1-2
issue with carb digestion in the stomach
too acidic
where is pancreatic juice secreted into during monogastric carb digestion
duodenum
T or F: pancreatic amylase cannot digest a (1,6) linkages
T
limit dextrins vs dextrins
limit dextrins are smaller but still have branch points
maltase
digests maltose to produce 2 glucose units
what is the only enzyme that can digest a (1,6) linkages? where is it located?
alpha-dextrinase
- brush border enzyme -> located on villi/microvilli
lactase
breaks down lactose to produce glucose & galactose
difference between lactose & sucrose
lactose has b (1,4) linkages
absorption of monosaccharides in monogastrics uses what 2 types of transport?
active & facilitated transport
basolateral membrane
where blood is flowing, nutrients are absorbed here
glucose is ( ) in concentration that galactose in monogastrics
higher
SLGT-1
receptor that is expressed in villi & microvilli
- function depends on presence of sodium
SLGT-1 uses GLUT ( ) to transport glucose from ( ) to ()
2, enterocyte, bloodstream
Na/K ATPase pump
pumps 3 Na out & 2 K in
what % of energy is dedicated to the Na/K ATPase pump
40-50%
how does glucose facilitated transport work
glucose concentration on luminal side is higher than in cell = move from high to low concentration (aka into bloodstream)
how is fructose transported into the cell?
uses GLUT 5 transporter to be facilitated inside cell then GLUT 2 to move to bloodstream
hydrolysis of ATP
ATP -> ADP
glucose is metabolized by the ( ) and released into ( ) to be used by other tissues
liver, peripheral circulation
how do galactose & fructose provide energy?
they get converted into glucose derivates via phosphorylation reactions so they can now enter glucose metabolic pathways
what 2 GLUT are most important for transporting glucose from bloodstream -> into cell
GLUT 2 & GLUT 4
where is SLGT-1 expressed?
only the small intestine
what GLUT is insulin dependent
GLUT 4
insulin is released in response to
glucose
what GLUT are insulin independent?
all but GLUT 4
GLUT 1
basic supply of glucose to cells
GLUT 2
low infinity transporter
glucose -> blood
GLUT 3
high affinity transporter for brain & other glucose dependent tissues
GLUT 4
insulin sensitive
muscle & tissues
GLUT 5
fructose
1 mol of glucose when completely oxidized yields ( ) mols of ATP
38
2 glucose fates
1) complete oxidation via glycolysis
2) fatty acid synthesis/energy storage
what kind of relationship is present between the rumen & its microorganisms
symbiotic
by-product of pre-gastric carb fermentation in ruminants
VFAs
structural carbs
mostly grazed, fermentative digestion allows nutrients to get energy from these
glucose metabolism to VFA yields ( ) mols of ATP
2-4
anaerobic vs aerobic conditions: ATP yields
anaerobic: 1 mol of glucose = 2-4 mols ATP
aerobic: 1 mol glucose = 38 mols ATP
what is produced when acetate & butyrate are produced
H ions
methane loss is associated with a significant energy loss of ( )
H
the more acetate & butyrate produced = more ( ) produced in rumen
methane
T or F: propionate does not produce H ions
T
why is it favourable to have more propionate in the rumen compared to acetate & butyrate?
less energy is wasted as methane
energy for ruminants comes from
fermentation
cellulolytic microorganisms
ferment fiber -> cellulose, hemicellulose, pectin
- produce acetate (acetate like fermentation)
- neutral pH bc more fiber = more chewing
amylolytic microorganisms
ferment starch
- produce propionate (propionate like fermentation)
- more acidic rumen
T or F: butyrate will always stay at same proportion but acetate & propionate will change
T
starch is ( ) fermentable than fiber which means more ( ) are produced
more, VFAs
90% of VFAs are absorbed in the
rumen
higher feed intake = more ( ) and less ( )
propionate, acetate
lower frequency of feeding = more ( ), less ( )
propionate, acetate
4 ways to increase acetate production in the rumen
1) feed more frequently
2) increase dietary forage
3) larger particle size
4) buffers
rumensin function
increase propionate production = decrease methane = increase feed efficiency
- prouce acetate type fermentation
gram ( ) bacteria decrease with rumensin
positive
how does rumensin prevent acidosis
decreases lactate
T or F: rumensin does not change stomach pH
T
how are VFAs absorbed?
across rumen wall into blood stream via passive & facilitated diffusion
once absorbed, acetate & butyrate are metabolized into ( )
ketone bodies
what ketone bodies are acetate & butyrate metabolized into?
B-hydroxybutyrate & acetoacetate
t or F: propionate is not metabolized in rumen epithelium during absorption
T
major function of propionate
produce glucose via gluconeogenesis
post-absorptive metabolism of VFAs (how do they each enter TCA cycle?)
acetate & butyrate: enter TCA cycle as acetyl CoA
propionate: enter TCA cycle as succinyl CoA
what is the only VFA that can produce glucose?
propionate
why would no propionate be shown in a blood sample?
bc all of it is extracted by the liver
what VFA is absorbed in the largest amounts
acetate
what is the major circulating energy substrate in ruminants vs monogastrics
r- acetate
m- glucose
oxaloacetate is used to produce
glucose
2 major fates of acetate & butyrate
1) generation of energy via TCA cycle
2) lipid synthesis
2 mol of acetate = ( ) ATP
24
what is the only gluconeogenic VFA
propionate
why are circulating blood glucose levels lower in ruminants than monogastrics?
glucose is reserved exclusively for vita functions like in the brain so they absorb very little glucose from small intestine and rely on gluconeogenesis for the glucose they need
bloat
viscous frothy foam in rumen that prevents eructation
2 causes of rumen acidosis
VFA accumulation
lactic acid accumulation
2 types of bloat
- frothy
- dry gas
frothy bloat
bacteria produces slime in rumen that traps gases
dry gas bloat
gas rises to space above digesta but animal is unable to release gas through eruptation
2 causes of dry gas bloat
- physical blockage of esophagus
- damage to vagus nerve -> no signal to brain for rumen contractions to get rid of gases
home remedy for bloat
vinegar
trochar
used to release gas in cows who have bloat
T or F: a trochar will not help with frothy bloat bc it needs an anti-foaming agent
T
how to treat frothy bloat
stomach tube anti-foaming agent
what is the digesta flowing into the stomach of monogastrics
amylopectin and dextrins
T or F: no complete digestion of amylopectin without alpha dextrins present
T
SARA
sub-acute ruminal acidosis
SARA is more common in ( ) cattle than ( ) cattle
dairy, beef
what is a major lactate producing bacteria in the rumen that may lead to SARA
strep. bovis
lactic acid promotes growth of ( ) which will produce lots of lactic acid in rumen = acidosis
lactobacilli
2 forms of lactic acid
1) L -> used by liver to produce glucose, can be metabolized
2) D: stays in bloodstream, cannot be metabolized
3 symptoms of SARA
1) reduced or erratic feed intake
2) reduced rumination
3) lameness
